U.S. patent number 9,159,897 [Application Number 14/047,029] was granted by the patent office on 2015-10-13 for superconducting structure having linked band-segments which are each overlapped by directly sequential additional band-segments.
This patent grant is currently assigned to Bruker HTS GmbH. The grantee listed for this patent is Bruker HTS GmbH. Invention is credited to Klaus Schlenga, Alexander Usoskin.
United States Patent |
9,159,897 |
Schlenga , et al. |
October 13, 2015 |
Superconducting structure having linked band-segments which are
each overlapped by directly sequential additional band-segments
Abstract
A superconducting structure (1) has a plurality of linked
band-segments (2), with each linked band-segment (2) having a
substrate (3) and a superconducting layer deposited onto it (4).
The linked band-segments (2) are joined to one another by
superconducting layers (4) that face each other. Each linked
band-segment (2) is joined to two additional band-segments (7a, 7b)
in such a way that the superconducting layers (4) of the two
additional band-segments (7a, 7b) and of the linked band-segment
(2) face each other. The additional band-segments (7a, 7b) together
substantially overlap the total length (L) of the linked
band-segment (2). This provides for a superconducting structure,
which exhibits high superconductivity and which is very suitable
for long distances.
Inventors: |
Schlenga; Klaus
(Linkenheim-Hochstetten, DE), Usoskin; Alexander
(Hanau, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Bruker HTS GmbH |
Hanau |
N/A |
DE |
|
|
Assignee: |
Bruker HTS GmbH (Hanau,
DE)
|
Family
ID: |
49274533 |
Appl.
No.: |
14/047,029 |
Filed: |
October 7, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140100119 A1 |
Apr 10, 2014 |
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Foreign Application Priority Data
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Oct 5, 2012 [DE] |
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10 2012 218 251 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
39/02 (20130101); H01L 41/06 (20130101); H01L
39/143 (20130101); H01L 39/248 (20130101) |
Current International
Class: |
H01B
12/00 (20060101); H01L 41/06 (20060101); H01L
39/02 (20060101); H01L 39/14 (20060101); H01L
39/24 (20060101) |
Field of
Search: |
;505/230,925,926 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 545 608 |
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Jun 1993 |
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EP |
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1 198 846 |
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Apr 2002 |
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EP |
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1 479 111 |
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Nov 2004 |
|
EP |
|
Primary Examiner: Wartalowicz; Paul
Attorney, Agent or Firm: Vincent; Paul
Claims
We claim:
1. A superconducting structure, comprising: a plurality of linked
band-segments, said plurality of linked band-segments having a
total length extending in an x-direction, each linked band-segment
having a substrate and a first superconducting layer deposited onto
said substrate, wherein linked band-segments which are adjacent to
each other in said x-direction are each separated from another by a
linked band-segment gap having a linked band-segment gap size in
said x-direction; and a plurality of additional band-segments
extending in said x-direction, wherein additional band-segments
which are adjacent to each other in said x-direction are each
separated from another by an additional band-segment gap having an
additional band-segment gap size in said x-direction which is
substantially equal to said linked band-segment gap size, each
additional band segment having a second superconducting layer,
wherein each of said linked band-segments is joined to two said
additional band-segments in such a way that said second
superconducting layers of said two additional band-segments and
said first superconducting layer of said linked band-segment face
each other, wherein said plurality of additional band-segments
substantially overlap said total length of said plurality of linked
band-segments but are displaced in said x-direction relative to
said linked band-segments such that each linked band-segment gap is
disposed proximate to a central region of an adjacent additional
band-segment and each additional band-segment gap is disposed
proximate to a central region of an adjacent linked band-segment,
said linked band-segments and said additional band-segments thereby
being disposed, structured and dimensioned such that electrical
current which is initially transported in said x-direction within a
first additional band-segment is subjected to a transverse current
flow in a z-direction, perpendicular to said x-direction, and into
a first linked band-segment, said transverse current flow having a
first maximum proximate to and downstream of a first linked
band-segment gap that neighbors and is upstream of said first
linked band-segment and a second maximum proximate to and upstream
of a first additional band-segment gap that neighbors and is
downstream of said first additional band-segment, said transverse
current flow having a first minimum proximate to and downstream of
said first additional band-segment gap and a second minimum
proximate to and upstream of a second linked band-segment gap that
neighbors and is downstream of said first linked band-segment.
2. The superconducting structure of claim 1, wherein the
superconducting structure comprises at least N sequential, linked
band-segments, where N.gtoreq.5, wherein at least one of said
additional band-segments is joined to two said linked
band-segments.
3. The superconducting structure of claim 2, wherein the
superconducting structure is constituted periodically along said
sequential, linked band-segments in a longitudinal direction of
said linked band-segments.
4. The superconducting structure of claim 1, wherein band-segments
of the superconducting structure are provided on an outside with a
shunt structure or are partially or completely enveloped in a shunt
layer.
5. The superconducting structure of claim 4, wherein two
band-segments which are joined by mutually facing superconducting
layers, do not overlap, in one or more overlap sections,
transversely with respect to a longitudinal direction of the
band-segments and that said shunt structure contacts an associated
band-segment, in at least one said overlap section.
6. The superconducting structure of claim 1, wherein the
superconducting structure further comprises two peripheral
band-segments, wherein each peripheral band-segment has a third
superconducting layer, wherein each said peripheral band-segment is
joined to said linked band-segment in such a way that said third
superconducting layer of said peripheral band-segment faces said
first superconducting layers of said linked band-segment, wherein
said linked band-segment substantially overlaps a total length of
said peripheral band-segment.
7. The superconducting structure of claim 6, wherein said two
additional band-segments overlap at least 95% of said total length
of said linked band-segments.
8. The superconducting structure of claim 1, wherein said linked
band-segments each have a length of at least 100 m.
9. The superconducting structure of claim 1, wherein the
superconducting structure has a total length of at least 1000
m.
10. The superconducting structure of claim 1, wherein a gap between
two said additional band-segments, which are joined to a same said
linked band-segment, has a gap width in a longitudinal direction of
said additional band-segments of 5 mm or less.
11. The superconducting structure of claim 1, wherein a gap between
two said additional band-segments, which are joined to a same said
linked band-segment is disposed approximately centrally with
respect to a length of that linked band-segment.
12. The superconducting structure of claim 1, wherein mutually
facing ends of two said additional band segments, which are joined
to a same said linked band-segment, taper toward each other or
taper to form a gap such that those two additional band segments
extend at an angle of between 5.degree. and 30.degree. with respect
to a longitudinal direction.
13. The superconducting structure of claim 1, wherein mutually
facing superconducting layers of joined band-segments are
contiguous or are joined to one another by one or more layers of
noble metal or by layers containing silver and/or one or more
layers containing copper or layers consisting of copper.
14. The superconducting structure of claim 1, wherein at least one
of said first and said second superconducting layers contains a
high-temperature superconducting material, YBCO or BSCCO.
15. The superconducting structure of claim 1, further comprising a
buffer layer or a buffer layer containing CeO2, disposed between
said substrate and at least one of said first and said second
superconducting layers.
Description
This application claims Paris convention priority of DE 10 2012 218
251.0 filed on Oct. 5, 2012, the entire disclosure of which is
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The invention relates to a superconducting structure, comprising a
plurality of band-segments of band-shaped superconductors, wherein
each band-segment has a substrate and a superconducting layer
deposited onto it, and wherein the band-segments are joined to one
another by superconducting layers that face each other.
US 2005/0173679 A1, for example, discloses such a superconducting
structure.
Superconductors can carry electrical currents practically without
any ohmic losses. They are especially deployed where high
electrical currents are required, for example, in magnet coils.
Superconductors can only conduct electrical current without losses
below a critical temperature (also called transition temperature).
Above this temperature, the superconductor enters a normally
conducting state.
Metal superconducting materials, such as NbTi, which can be
processed as wires, have a relatively low critical temperature (for
NbTi, for example, it is about 9K), making their use quite
expensive, especially with respect to the necessary cooling.
Moreover, metal superconductors have relatively low critical
magnetic fields, above which they lose their superconductive
properties.
High-temperature superconductors (HTSL), such as yttrium barium
copper oxide (YBCO), have significantly higher critical
temperatures, YBCO for example, about 90K, but are difficult to
process due to their ceramic properties. If they are used at
temperatures significantly below their critical temperature, HTSLs
can conduct comparatively large currents, i.e. they have a high
critical current density. With their comparatively high critical
magnetic field strengths, these materials are also suitable for low
operating temperatures in strong magnetic fields.
For technical applications, HTSLs are usually deposited as a thin
layer onto band-shaped, usually metal substrates, wherein, as a
rule, one or more buffer layers are interposed between the
substrate and the superconducting layer, and one or more final
metal layers are deposited on top of the superconducting layer.
This type of construction is also termed a band-shaped
superconductor and has commonly become known as a "coated
conductor" in English.
However, depositing superconducting layers of good quality is
relatively difficult. As a rule, substrate surfaces with a special
texture are required, which can only be provided over limited
lengths. Currently, good-quality band-segments of band-shaped
superconductors are limited to a maximum range of approx. 100 to
200 m.
EP 0 545 608 A2 proposes joining conductor segments, which can only
be manufactured in good quality in limited lengths, in order to
enable current to be transported over longer distances, for
instance, several kilometers.
US 2005/0173679 A1 discloses the joining of two band-segments of
band-shaped superconductors, wherein the superconducting layers on
the respective substrates face each other. The superconducting
layers are to be in superconducting contact and the proximity of
the two polycrystalline superconducting layers is intended to
increase the effective grain boundary surface and thus improve the
critical current.
U.S. Pat. No. 6,828,507 B1 also discloses the joining together of
two band-segments of band-shaped superconductors, wherein the
superconducting layers on the respective substrates face each
other. The superconducting layers are joined by means of one or
more normally conducting intermediate layers (for instance,
covering layers of the individual band-segments).
The object of the invention is to provide a superconducting
structure, which exhibits a high current-carrying capacity and
which is also suitable for long distances.
SUMMARY OF THE INVENTION
This object is achieved with a superconducting structure of the
type mentioned in the introduction, characterized in that a
plurality of the band-segments are each constituted as a linked
band-segment, wherein each linked band-segment is joined to two
additional band-segments in such a way that the superconducting
layers of the two additional band-segments and of the linked
band-segment face each other, and that the additional band-segments
together substantially overlap the total length of the linked
band-segment.
The inventive superconducting structure exhibits a particularly
high current-carrying capacity. Electrical current can cross
between opposite band-segments. If the critical current density is
inhomogeneous (for instance, due to normally conducting defect
regions in a superconducting layer) in any one of the
band-segments, the latter are bridged by their opposite
band-segment and vice versa, so that such inhomogeneities do not
cause any noticeably diminished current-carrying capacity of the
superconducting structure overall.
Furthermore, the contact surfaces between opposite band-segments
are very large: according to the invention, practically the entire
length of a linked band-segment is used for transverse current
crossing, which makes the contact resistance very small. In
particular, it is possible to provide one or more layers of
normally conducting material between opposite superconducting
layers, without the ohmic resistance noticeably increasing.
Nonetheless, these normally conducting layers should be made of
materials exhibiting good electrical conductivity (for example,
noble metals or copper or alloys thereof), and the thickness of the
layers should be relatively small. These intermediate layers can
simplify the manufacturing process of the superconducting structure
and assist as heat conductors and parallel current paths to the
superconducting layers to stabilize superconductivity and provide
quench protection.
According to the invention, it is possible to keep ohmic cable
resistance to negligible levels even if a large number of
band-segments are sequentially linked. This also makes the
invention very suitable for transmitting current over long
distances, for example, in the kilometer range.
The additional band-segments, with which a linked band-segment is
joined according to the invention, can also be linked
band-segments; in this way practically any lengths can be
constructed with the inventive superconducting structure.
According to the invention, the joining of two band-segments to
mutually facing (opposite) superconducting layers results in
superconducting or quasi superconducting electrical contact, so
that, at least along the overlap, a negligible overall ohmic
resistance occurs.
In a preferred embodiment of the inventive superconducting
structure, the superconducting structure comprises at least N
sequential, linked band-segments, where N.gtoreq.5, preferably
N.gtoreq.20, in such a way that at least one of the additional
band-segments associated with each one of the sequential, linked
band-segments is itself a sequential, linked band-segment. In this
way, the superconducting structure and its advantages can be used
over any distance, in particular, over long distances. For all the
inner band-segments (inner with respect to the longitudinal
direction) of the sequential, linked band-segments, each of the two
additional band-segments are linked band-segments and, for the two
outer band-segments of the sequential, linked band-segments, only
one of the additional band-segments is a linked band-segment. The
superconducting structure of this variant always comprises
band-segments in two planes (upper and lower plane). The linked
band-segments in the upper plane are disposed sequentially with
their superconducting layers oriented downward, and the linked
band-segments in the lower plane are also disposed sequentially but
with their superconducting layers oriented upward.
In a preferred variant of this embodiment, the superconducting
structure is constituted periodically along the sequential, linked
band-segments in the longitudinal direction of the band segments.
This makes the structure especially simple; in particular,
band-segments of the same length can be integrated.
An embodiment is also preferred in which the superconducting
structure has two peripheral band-segments, wherein one peripheral
band-segment is joined to a linked band-segment in such a way that
the superconducting layers of the peripheral band-segment and of
the linked band-segment face each other, and the linked
band-segment substantially overlaps the total length of the
peripheral band-segment. The superconducting structure can be
terminated at both ends (front and rear end) with the peripheral
band-segments. The peripheral band-segments can be disposed in the
same plane or in different planes. Typically, the linked
band-segment overlaps at least 95%, preferably at least 99%, or
also 100% of the length of the peripheral band-segment.
In an especially preferred embodiment of the inventive
superconducting structure, the two additional band-segments
together overlap at least 95%, preferably at least 99% of the total
length of a linked band-segment. In this way, a very large contact
surface between the overlapping band-segments and a correspondingly
small electrical resistance can be achieved. Any remaining
(non-overlapping) length of the linked band-segment typically
corresponds to a gap between the additional band-segments, and/or
to entry or exit points for the electrical current (which are then
usually at the ends of the superconducting structure).
An embodiment is also preferred, in which the linked band-segments
each have a length of at least 100 m, preferably at least 200 m. On
the one hand, this also ensures that the overlapping lengths with
the additional band-segments are also large (usually approximately
half of the length of the linked band-segment for each additional
band-segment), on the other hand, with band-segment lengths of this
size it is possible to efficiently constitute a large total length
of the superconducting structure.
Also preferred is an embodiment, in which the superconducting
structure has a total length of at least 1000 m, preferably at
least 2000 m. The inventive superconducting structure can provide
such large total lengths without any problem; the advantages of the
invention are then especially apparent.
In an advantageous embodiment, a gap between two additional
band-segments, which are joined to the same linked band-segment,
has a gap width in the longitudinal direction of the band-segments
of 5 mm or less, preferably 2 mm or less, in particular, wherein
the gap is closed with abutting additional band-segments. Due to
the small or even negligible gap width, it is very unlikely that an
inhomogeneity of the critical current density in the linked
band-segment will happen to be located beneath the gap.
An embodiment is also preferred, in which the gap between two
additional band-segments that are joined to the same linked
band-segment are disposed approximately in the center of the length
of this linked band-segment. By disposing the gap in the center,
the contact surfaces with the additional band-segments have
approximately the same partial length available to them, wherein a
one-sided increase of the contact resistance with one of the
additional band-segments is avoided. Typically, the gap position
deviates by no more than 10%, preferably by no more than 5%, from
the center of the linked band-segment, with reference to the length
of the linked band-segment.
In an advantageous embodiment of the inventive superconducting
structure, the mutually opposite ends of two additional
band-segments, which are joined to the same linked band-segment,
each taper toward the other additional band-segment, in particular,
so that a gap between these two additional band-segments, at least
in sections, extends at an angle of between 5.degree. and
30.degree. with respect to the longitudinal direction of the
band-segments. In this variant, the gap between the additional
band-segments, at least in sections, extends obliquely (and in
particular, not perpendicularly) with respect to the longitudinal
direction of the linked band-segment. The gap extends a
considerable distance (in the longitudinal direction of the linked
band-segment), but at no point extends over the full width of the
superconducting structure. In this way, inhomogeneities of the
critical current, which do not usually extend over the full width
of a superconducting layer (cf. typical bandwidths of between 2 mm
and 6 cm) can regularly easily be bridged, even if they are located
in the vicinity of the gap.
An embodiment is also preferred, in which mutually facing
superconducting layers of linked band-segments are contiguous, or
are joined to one another by one or more layers of noble metal, in
particular, layers containing silver, and/or one or more layers
containing copper, in particular layers consisting of copper. If
they are contiguous, very good (even superconducting) contact can
always be established between the superconducting layers; however,
the joining technology is difficult to master. If they are joined
by means of a normally conducting layer (or a plurality of such
layers), production of the superconducting structure is simpler,
and the layers can be used to perform a function (for example,
stabilization or quench protection). Due to the large contact
surfaces, only a negligible ohmic resistance occurs through the
normally conducting layer (or through a plurality of such layers)
if suitable material (with sufficiently high electrical
conductivity) and a suitable layer thickness (not too thick) are
chosen.
An embodiment is also advantageous, in which the band-segments of
the superconducting structure are provided on the outside with a
shunt structure, in particular, partially or completely enveloped
in a shunt layer. In this way, a normally conducting current path
is provided that extends parallel with the superconducting layers
which, in the case of a sudden collapse of the superconductivity
("quench"), can take over the previously superconductively carried
electrical current. In this way, overheating ("melting through") of
the superconducting layers can be avoided. In particular, the shunt
structure can be made of copper.
In a preferred further embodiment, two band-segments, which are
joined by mutually facing superconducting layers, do not overlap,
in one or more overlap sections, transversely with respect to the
longitudinal direction of the band-segments, and that the shunt
structure contacts the associated band-segment in at least one said
overlap section. In this way, conduction of electrical current out
of the superconducting layers of the band-segments is particularly
easy if a quench occurs. Two overlap sections can occur as the
result of the offset of two equally wide band-segments that extend
transversely with respect to the longitudinal direction of the
band-segments; one or two overlap sections can result by using
band-segments of different widths.
An embodiment is especially preferred in which the superconducting
layer contains a high-temperature superconducting material, in
particular, YBCO or BSCCO. HTSL material allows operation at high
temperatures (for example, with LN.sub.2 cooling), which saves
maintenance costs, or a particularly high current-carrying capacity
can be achieved (at lower temperatures, particularly with LHe
cooling). Within the scope of the invention, HTSL materials are
considered to be any materials with a critical temperature above
40K. BSCCO materials can comprise
Bi.sub.2Sr.sub.2CaCu.sub.2O.sub.8+x and/or
Bi.sub.2Sr.sub.2Ca.sub.2Cu.sub.3O.sub.10+x.
Also advantageous is an embodiment, in which a buffer layer, in
particular, containing CeO2, is disposed between the substrate and
the superconducting layer. In this way, the quality of the
superconducting layer can be improved. It is also possible to use
multiple buffer layers.
The scope of this invention also includes a method for transporting
electrical current along a superconducting structure, comprising a
plurality of band-segments of band-shaped superconductors, in
particular, along an inventive superconducting structure described
above, wherein each band-segment comprises a substrate and a
superconducting layer deposited onto it,
and wherein the current crosses between the band-segments, for
which a transverse current flows,
which is characterized in that transverse current essentially flows
along the entire length of the superconducting structure, with the
exception of local regions
of gaps between sequential band-segments that are in the same plane
of the superconducting structure and of positions of a local
inhomogeneity of the critical current. By providing transverse flow
of current along what is essentially the entire length of the
superconducting structure, contact resistance between the involved
band-segments is minimized. It is important to observe that,
according to the inventive method, in many regions of the surface
of a superconducting layer, a net transverse current of "zero"
certainly can flow, which does not mean, however, that no
transverse current flow occurs here, only that the magnitude of the
transverse current flowing in one direction is equal to that
flowing in the opposite direction; in such regions of the surface,
a transverse current indeed flows for the purpose of the inventive
method. At gaps and regions of inhomogeneity (for example, normally
conducting defect regions in the superconducting layers of the
band-segments), the transported electrical current is redirected
via a bridging band-segment due to suitable transverse current
flows in front of and behind the gap or the inhomogeneity, so that
high current-carrying capacities of the superconducting structure
can be achieved according to the inventive method. It is important
to note that gaps are typically very much smaller than the length
of a band-segment, with gap widths of typically 5 mm or less,
preferably 2 mm or less, and typical lengths of a band-segment
bridging the gap of 100 m or more, preferably 200 m or more.
In a preferred variant of the inventive method, more than 99%,
preferably more than 99.999% of the electrical current transported
along the superconducting structure crosses between band-segments,
which are joined to each other by mutually facing superconducting
layers. According to the variant, most of the current by far is
transported in the superconducting layers, which participate in the
crossing of the current between different band-segments, whereby
the advantages of the invention are particularly apparent.
Equally preferred is a variant, in which, on one linked
band-segment that joins two sequential, additional band-segments in
one plane across a gap located between these band-segments, the net
transverse current that flows to and from the additional
band-segments has a local maximum in the region of the first end of
the linked band-segment, a further local maximum in the region just
in front of a gap of the two additional band-segments, a local
minimum in the region just behind the gap of the two additional
band-segments, and finally a further local minimum in the region of
the second end of the linked band-segment, or vice versa. With this
transverse current profile, the transported current can be
efficiently redirected in front of a gap. In the case of oblique
gaps, the extrema in the vicinity of a gap are usually less
pronounced.
Further advantages result from the description and the drawing.
Moreover, the features stated above and further below can be used
singly or together in any combination. The embodiments shown and
described are not intended to be an exhaustive list, rather are
examples to explain the invention.
The invention is shown in the drawing and is explained in more
detail using the example of the embodiments. The figures show:
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 a schematic longitudinal section through a periodic part of
an inventive superconducting structure;
FIG. 2 a schematic longitudinal section through an inventive
superconducting structure with five linked band-segments and two
peripheral band-segments;
FIG. 3a a schematic oblique view onto part of an inventive
superconducting structure in the region of a gap that extends
transversely with respect to the longitudinal direction;
FIG. 3b a schematic oblique view onto part of an inventive
superconducting structure in the region of a gap that extends
obliquely with respect to the longitudinal direction;
FIG. 4a-4f schematic cross-sections through different embodiments
of an inventive superconducting structure; and
FIG. 5 a diagram schematically illustrating the transverse current
through a linked band-segment or an inventive superconducting
structure as a function of the location along the longitudinal
direction of the superconducting structure.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a cutout view in a schematic longitudinal section of a
portion of inventive superconducting structure 1. The
superconducting structure 1 has a plurality of band-segments of
band-shaped superconductors, wherein the cutout view of the figure
only comprises so-called linked band-segments 2. The sectional view
shows a total of eleven sequential, linked band-segments 2 shown
either partially or in their entirety (for the purposes of
simplification, only one of the band-segments is marked with
reference number 2 in the figure).
Each band-segment 2 has a substrate 3 (for instance, made of sheet
steel) and a superconducting layer 4 deposited on the substrate 3.
The band-segments 2 are disposed in two planes E1, E2; the
band-segments 2 in the upper plane E1 are oriented with their
superconducting layers 4 facing downward (toward the lower plane
E2), and the band-segments 2 in the lower plane E2 are oriented
with their superconducting layers 4 facing upward (toward the upper
plane E1). A layer 5 of solder, which here consists of an alloy
containing silver, is disposed between the band-segments 2 of the
different planes E1, E2.
Between each of the adjacent band-segments 2 in the same plane E1,
E2 in the depicted embodiment, there is a gap 6 with a gap width SP
that is very much smaller than length L of the band-segments 2. In
the sectional view shown, the superconducting structure 1 has a
periodic structure in the longitudinal direction (x-direction) (in
both planes E1, E2 and in total); in particular, all linked
band-segments 2 here have the same length L and the gaps 6 have the
same gap width SP.
It is important to observe that the dimensions in FIG. 1 (and in
the subsequent figures) are not to scale and many of the structural
elements are shown enlarged to make it easier to distinguish them.
In the longitudinal direction x of the superconducting structure 1,
the band-segments 2 typically have a length L of ten meters or
more; gap widths SP (in the x direction) are typically 5 mm or
less. The width of the band-segments 2 perpendicular to the drawing
plane of FIG. 1 (y direction) are typically between 2 mm and 6 mm,
and the height of the band-segments 2 in the z direction is
typically in the range 200 .mu.m or less, usually approx. 100 .mu.m
or less. The thickness of a superconducting layer 4 (in the z
direction) is usually several .mu.m, and the thickness of a typical
solder layer 5 is usually in the 100 .mu.m range or less, often 25
.mu.m or less.
The superconducting structure 1 is used to transport an electrical
current in its longitudinal direction x. For that reason, the
band-segments 2 are inventively constituted as linked band-segments
2. Each linked band-segment 2 overlaps in the x direction with two
additional band-segments 7a, 7b (which themselves are linked
band-segments here). In this case, the length L of the linked
band-segment 2 is more of less fully overlapped by the two
band-segments 7a, 7b combined; only in the region of gap 6 between
the additional band-segments 7a, 7b is there no overlap in the
embodiment shown. The gap 6 is centrally positioned with respect to
the linked band-segment 2, so that the lengths overlapping with the
band-segments 7a, 7b are each approximately L/2.
An electric current to be transported in the longitudinal direction
of superconducting structure 1 (x direction) in the additional
band-segment 7a (and/or its superconducting layer 4) can cross into
the linked band-segment 2 over a very large surface (transverse
current flow in the z direction), before the gap 6 blocks further
current flow in the longitudinal direction. The ohmic resistance at
this crossover point is correspondingly low. In the linked
band-segment 2, the current flow can then cross the gap 6. The
current can then similarly cross into the additional band-segment
7b, in order to bridge the next gap, and so forth.
FIG. 2 also shows an inventive superconducting structure 1 in a
longitudinal section with exactly five linked band-segments 2 and
two peripheral band-segments 8a, 8b; the superconducting structure
1 extends in the x direction. The gaps 6 between the adjacent
band-segments 2, 8a, 8b within the two planes E1, E2 have a
negligible gap width (in the x direction) in this embodiment.
The superconducting layers 4 of the left and right outer linked
band-segments in the upper plane E1 each face toward one of the
peripheral band-segments 8a, 8b and toward a linked band-segment 2
as additional band-segments 7a, 7b, or they are joined thereto by
means of the layer 5 of solder. The peripheral band-segments 8a, 8b
are here fully overlapped by their respective opposite outer linked
band-segment 2 in the x direction.
The embodiment shown also has a buffer layer 9 of the band-segments
2, 8a, 8b, which, for example, contains CeO2 and is disposed
between the substrate 3 and the superconducting layer 4.
FIG. 3a shows a schematic oblique view of a sectional view of an
inventive superconducting structure 1, for example, of a
superconducting structure as shown in FIG. 1, in the region of a
gap 6 between two adjacent, linked band-segments 2 in the upper
plane of the superconducting structure 1; these two band-segments
represent additional band-segments 7a, 7b of band-segment 2 in the
lower plane. In the embodiment shown, the gap 6 extends
transversely (perpendicularly) with respect to the longitudinal
direction x of the superconducting structure 1; this gap geometry
is particularly easy to produce.
However, it is also possible to constitute the gap 6 obliquely with
respect to the longitudinal direction (x direction), as is shown in
the superconducting structure 1 of FIG. 3b. The ends 10a, 10b of
the band-segments 2 and 7a, 7b respectively in the upper plane of
the superconducting structure 1 here each taper toward the other
band-segment 2 and/or 7b, 7a; the ends 10a, 10b expand more or less
to the full width B of the two band-segments 2 and 7a, 7b
respectively. The remaining gap 6 largely extends at an angle
.alpha. of approx. 15.degree. with respect to the longitudinal
direction x.
According to the invention, a gap width SP is always measured in
the longitudinal direction x, even if the gap 6 extends obliquely
with respect to the longitudinal direction x. If the gap width
along gap 6 varies, the gap width SP of the gap overall is always
determined by the largest gap width occurring along the gap 6.
FIGS. 4a to 4f show cross sections (cf. plane IV in FIG. 1) of
various embodiments of inventive superconducting structures 1,
wherein the cross section is selected at a position away from the
gaps.
As can be seen in FIG. 4a, the opposite, here equally wide,
band-segments 2 of an inventive superconducting structure 1, can be
disposed offset with respect to each other (in the y direction) in
such a way that two overlapping sections 13 remain transverse with
respect to the longitudinal direction x. The latter are contacted
with two shunt elements 11a, 11b, preferably made of copper, so
that two normally conducting current paths are established parallel
to the superconducting layers 4, to constitute a shunt structure
12. A solder containing silver is provided for a good electrical
contact between the superconducting layers 4 (however, here not
below the shunt elements 11a, 11b).
In the embodiment of the superconducting structure 1 shown in FIG.
4b, two band-segments 2 of different widths are integrated. The
thinner, upper band-segment 2 is placed in the center of the lower,
wider band-segment 2 and is enveloped in a shunt layer 14, which
also covers the overlap sections 13 of the lower band-segment 13.
In the embodiment shown, the shunt layer 14 (which is preferably
made of copper) contacts with a solder layer 5, whereby good
electrical contact with both superconducting layers 4 is assured.
In this way, the shunt layer 14 can be deployed as the shunt
structure 12 for both band-segments 2.
In the embodiment of the superconducting structure of FIG. 4c, the
two opposite band-segments 2, which are however laterally displaced
with respect to each other are fully enveloped in a shunt layer 14,
which correspondingly also contacts with the overlap section 13
(here, by means of the solder layer 5). The shunt layer 14 here not
only acts as the shunt structure 12 but also as a mechanical
bracket for both band-segments 2.
FIG. 4d shows a variant of the embodiment of FIG. 4a, wherein an
additional shunt layer 14, which is L-shaped, surrounds the two
shunt elements 11a, 11b and the upper band-segment 2. In this way,
the cross-section surface of the entire shunt structure 12 can be
increased.
It is also possible to only partially overlap a band-segment 2
disposed below in FIG. 4e with an upper band-segment 2 laterally in
the y direction so that an overlap section 13 remains, and to
contact this overlap section 13 with an auxiliary band-segment 15.
The auxiliary band-segment 15 can but does not have to be a linked
band-segment of the superconducting structure 1. The auxiliary
band-segment 15 forms an auxiliary overlap section 13a, which can
be contacted with a shunt element 11, wherein practically any width
(in the y direction) of the auxiliary overlap section 13a can be
defined by the width of the auxiliary band-segment 15. This can be
used to set the power of the shunt configuration 12.
Moreover it is possible to constitute a shunt configuration 12 with
two shunt layers 14a, 14b (here made of copper), which each
separately envelops one of the two band-segments 2, and to join the
two shunt layers 14a, 14b by means of a solder layer 5, cf. FIG.
4f. As a result, two copper layers 14c, 14d, and a solder layer 5,
here made of silver, effectively lie between the facing
superconducting layers 4 of the two band-segments 2.
FIG. 5 illustrates the flow of electrical current 50 transported in
an inventive superconducting structure 1 in the longitudinal
direction x. The superconducting structure 1 comprises at least one
linked band-segment 2 and two additional band-segments 7a, 7b
joined to the latter, which overall overlap the band-segment 2
along its entire length in the x direction up to a gap 6 extending
in the y direction. In the diagram, the transverse current flow
I.sub.z, that is, the current flowing in the z direction
perpendicularly into the superconducting layer 4 of the
band-segment 2 (or out of it if the sign is negative), is shown as
a function of the x position. For the sake of clarity, the
band-segments 2, 7a, 7b in the upper part of the figure are
depicted more spread out.
The transverse current I.sub.z initially has a maximum Max1 in the
vicinity of the left end 51, as shown in FIG. 5, of the
band-segment 2 because in this region the current flowing from the
left through the additional band-segment 7a can for the first time
reach the band-segment 2 and utilize it. Finally, in front of gap 6
all (remaining) current from the additional band-segment 7a must
cross into the band-segment 2, which results in a further maximum
Max2. It is important to note that Max1 and Max2 are typically
equally large. No transverse current flow is possible directly
above the gap 6 between the two additional band-segments 7a, 7b
(which have the same position with respect to z, i.e. are in the
same plane). Beyond the gap 6, current can, for the first time,
flow into the additional band-segment 7b, which results in a first
minimum Min1 of the transverse current I.sub.z. Just in front of
the right end 52 of the band-segment 2, all the (remaining) current
must finally cross into the additional band-segment 7b, which can
be recognized by the additional minimum Min2.
Similarly to a gap 6, any inhomogeneity of the critical current
(for example, a normally conducting defect region in a
superconducting layer 4) can be bypassed by the current 50.
An inventive superconducting structure can, in particular, be used
in superconducting cables or in superconducting magnet coils.
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